At some point life "got in the way", and between a kid and a full-time job my gym time started to disappear. I've tried a lot of creative approaches to keeping fit with shorter workouts, and what I have come up with isn't all that different than what is being prescribed here.
My basic approach is this:
1. Pushups - every other morning I do 5 minutes of pushups where I start at a set of 20 then bump up by a count of 5 until I'm at 35. Then I work my way back down to 20 allowing brief 20 second rests in between.
2. Pullups - same as pushups except I start at 6 and bump by 2 until I hit 10, and then work back down.
3. Squats - No weight, three sets of 50. This could be better, but I'm kinda lazy when it comes to squats
4. Mix in exercises using resistance bands. (shoulder press, lat pulls, tricep extensions, etc). I usually do these in three sets of 12-15.
Each workout takes about 15 minutes, and while I've lost some muscle mass I'm still a pretty lean/muscular 170. I'm sure there are all sorts of optimizations I could make, but honestly I don't really care at this point. I've found a quick workout I can do 3-4 times a week and it is keeping me pretty damn healthy.